Sources: Texas Tech's Gill-Howard out indefinitely

Texas Tech defensive tackle Skyler Gill-Howard underwent ankle surgery on Thursday in Dallas and is out indefinitely, sources confirmed to ESPN.

Gill-Howard, a Northern Illinois transfer who has been a standout for the No. 7 Red Raiders and one of the top defenses in college football, suffered the injury during their win over Kansas last Saturday. The injury has not been determined to be a season-ending one at this time, sources told ESPN, and there's hope Gill-Howard could return for the postseason.

The 6-foot-1, 290-pound senior has played in six games and has recorded 13 tackles, 2.5 tackles for loss and an interception that he returned 55 yards for a touchdown against Kent State. Texas Tech has the No. 1 run defense in FBS at 62.5 rushing yards per game and the No. 6 scoring defense, allowing 12.2 points per game.

Houston transfer A.J. Holmes Jr. is expected to replace Gill-Howard in the starting lineup, sources told ESPN, and Texas Tech coaches are expecting senior backup E'Maurion Banks is play a more significant role going forward.

The Red Raiders, 6-0 for the first time since 2013, face defending Big 12 champion Arizona State in a road test on Saturday (4 p.m. ET, FOX).

CBS Sports first reported that Gill-Howard is expected to miss significant time.